1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device which can control a viewing angle, and a method of manufacturing the same, and more particularly, to a fringe field switching (FFS) mode LCD device.
2. Discussion of the Related Art
Liquid crystal displays, especially, liquid crystal displays adopting thin film transistors (TFT) have been widely used in various applications from mobile phones to large-sized televisions.
One of them is a personal display device, the display screen of which is required to be seen by a user of the personal display device but not to be seen by other persons who view the personal display device from the side.
Preferably, the personal display device is constructed such that the display screen of the personal display device can be viewed by a large number of persons or the display screen can be exclusively used by only one individual as occasion demands.
FIG. 11 is a schematic drawing illustrating a related art LCD device having a secret mode.
There has been proposed a display having the secret mode shown in FIG. 6 (for example, Japanese Unexamined Publication No. 5-72529).
Referring to FIG. 11, when using a backlight which emits light to the rear surface of a liquid crystal display panel, it necessarily requires the backlight having the high directivity.
Between the common liquid crystal display panel and the backlight having the high directivity, there is another liquid crystal display panel for switching between a scattered state and an unscattered state, for example, a polymer dispersed type liquid crystal display panel (a scattering-unscattering switching layer).
When the scattering-unscattering switching layer is in an unscattered state, the light emitted from the backlight proceeds only to the front direction. Thus, if the person is positioned at the side of the liquid crystal display panel, it is impossible for the person positioned at the side to view the displayed image.
On the other hand, if the scattering-unscattering switching layer is in a scattered state, the light emitted from the backlight proceeds to the side directions as well as the front direction. Thus, even though the person is positioned at the side of the liquid crystal display panel, it is possible to view the displayed image. Consequently, a large number of persons can view the image displayed on the liquid crystal display panel.
In this case, it is necessary to fabricate a special liquid crystal display panel which is different from the common liquid crystal display panel. Therefore, the manufacturing costs are increased.
In order to solve this problem, there has been proposed a method using a vertical alignment type liquid crystal display device. Hereinafter, the vertical alignment type liquid crystal display device is explained with reference to FIGS. 12 to 15.
Hereinafter, the fundamental principle thereof will be described in detail with reference to FIGS. 12 to 15.
FIGS. 12A and 12B are schematic drawings illustrating the shape of liquid crystal molecule when viewing the vertical alignment type liquid crystal display device from the front side.
In a state that the voltage is not applied to the liquid crystal display panel as shown in FIG. 12A, the liquid crystal molecule is aligned vertically. When the voltage is applied to the liquid crystal display panel as shown in FIG. 12B, the liquid crystal molecule is inclined upward. In this case, a polarizer has its axis directed in the vertical direction, and an analyzer has its axis directed in the horizontal direction.
FIG. 12A illustrates a case that the vertically aligned liquid crystal display panel, to which the voltage is not applied, is viewed from the front. According as the birefringence of the liquid crystal molecule does not occur, any light is not transmitted.
On the other hand, FIG. 12B illustrates a case that the vertically aligned liquid crystal display panel, to which the voltage is applied, is viewed from the front. The optical axis of the liquid crystal molecule is in parallel with the absorption axis of the polarizer. Also, birefringence of the liquid crystal molecule does not occur, and any light is not transmitted.
FIGS. 13A and 13B are schematic drawings illustrating the shape of a liquid crystal molecule when viewing the vertical alignment type liquid crystal display device from the side at an angle to the front of the liquid crystal display device.
When the voltage is not applied, as shown in FIG. 13A, the axis of the liquid crystal molecule is in parallel with the absorption axis of the analyzer, and therefore, the light is not transmitted.
On the other hand, when the voltage is applied, as shown in FIG. 13B, the axis of the liquid crystal molecule is offset from the axis of the polarizer or the axis of the analyzer. Consequently, birefringence of the liquid crystal molecule occurs, and light is transmitted.
When the light leakage phenomenon is used, the display contrast is lowered to the extreme in the horizontal (left and right) direction. As a result, it is impossible to recognize what is written even when the display is seen from a horizontal direction. Consequently, it is possible to control the confidentiality of the display using this light leakage phenomenon.
FIG. 14 is a a schematic drawing illustrating the specific construction for controlling the confidentiality of the display. In FIG. 14, a single pixel includes sub-pixels of red, green and blue (RGB) and a sub-pixel of white (W).
FIG. 15 is a plan view illustrating the arrangement of liquid crystal molecules of the respective sub-pixels shown in FIG. 14. As shown in FIG. 15, the alignment of the liquid crystal molecules in the white sub-pixel is quite different from the alignment of the liquid crystal molecules in the RGB sub-pixels.
Consequently, when the voltage is not applied to the white sub-pixel, the white sub-pixel does not contribute to the display, whereby a normal display can be realized.
When the voltage is applied to the white sub-pixel, the white display is performed at the front in the horizontal (left and right) direction. As a result, the contrast of the display is lowered in the horizontal (left and right) viewing angle direction, and therefore, it is difficult for other people to view the displayed image.
Hereinafter, a fringe field switching (FFS) mode LCD device, which includes a common electrode in shape of “<” to improve a viewing angle, will be explained as follows.
FIG. 16 is a plan view illustrating each of RGB pixels for a related art FFS mode LCD device. FIGS. 17A and 17B are schematic drawings illustrating the operation of liquid crystal molecules according as the voltage is applied to a related art FFS mode LCD device or not.
As shown in FIG. 16, the related art FFS mode LCD device includes a common electrode which is formed in shape of “<”, so as to regulate the inclination direction of liquid crystal.
As shown in FIG. 17A, if the voltage is not applied to the LCD device, the liquid crystal molecules are aligned in the vertical direction. If the voltage is applied to the LCD device, the liquid crystal molecules are inclined in the predetermined direction decided based on the effect of the inclined electric field by the common electrode, that is, the direction perpendicular to the extending direction of the common electrode, as shown in FIG. 17B. As a result, the liquid crystal molecules are inclined to the two directions corresponding to a chevron “<” shape, whereby the LCD device has the good viewing angle.
However, the related art LCD device has the following problems.
First, the related art LCD device is constructed such that the white sub-pixel is formed; however, it is necessary to newly form a white resin, and the driving operation of the white sub-pixel is different from the related art.
Even though the visibility for the specific direction in the LCD device can be improved owing to the “<”-shaped common electrode, it is impossible to obtain the display of confidentiality on occasion demands.